In drilling wellbores through subsurface formations, e.g., for extraction of materials such as hydrocarbons, a rotating control device (RCD) is directly or indirectly mounted on the top of a wellhead or a blowout preventer (BOP) stack. The BOP stack may include an annular sealing element (annular BOP), and one or more sets of “rams” which may be operated to sealingly engage a pipe “string” disposed in the wellbore through the BOP or to cut the pipe string and seal the wellbore in the event of an emergency.
The RCD is an apparatus used for well operations which diverts fluids such as drilling mud, surface injected air or gas and other produced wellbore fluids, including hydrocarbons, into a recirculating or pressure recovery “mud” (drilling fluid) system. The RCD serves multiple purposes, including sealing tubulars moving in and out of a wellbore under pressure and accommodating rotation and longitudinal motion of the same. Tubulars can include a kelly, pipe or other pipe string components, e.g., parts of a “drill pipe string” or “drill string”.
Typically, a RCD incorporates three major components that work cooperatively with one another to hydraulically isolate the wellbore while diverting wellbore fluids and permitting a pipe string (e.g., a string) to rotate and move longitudinally while extending through the RCD. An outer stationary housing having an axial bore is hydraulically connected to the wellhead or BOP. The outer stationary housing can have one or more ports (typically on the side thereof) for hydraulically connecting the axial bore of the housing to return flow lines for accepting return wellbore fluids. A bearing assembly is replaceably and sealingly fit within the axial bore of the outer housing for forming an annular space therebetween.
The bearing assembly comprises a rotating inner cylindrical mandrel replaceably and sealingly fit within a bearing assembly housing. An annular bearing space is formed between the rotating inner cylindrical mandrel and the bearing assembly housing for positioning bearings and sealing elements. The bearings permit the mandrel to rotate within the bearing assembly housing while the sealing elements isolate the bearings from wellbore fluids.